For a rifle to shoot to its maximum potential accuracy the barrel needs to resonate at its natural pitch, to do that it must be free floating.

Therefore the barrel should not touch in the barrel channel at any point in front of the chamber, and in a lot of cases, it should not touch at all. This is even more important if you shoot from a bipod as the vibration from the shot often closes the gap between the barrel channel and the barrel during recoil.

It is a simple job to open the channel to free float the barrel, but is often overlooked and is detrimental to accuracy if not addressed.